1. Field of the Invention
The present invention relates to a solid polymer electrolyte type fuel cell system.
2. Description of Related Art
Conventionally, when it is required to increase the supplying pressure of reaction gas to be supplied to a solid polymer electrolyte type fuel cell, reaction gas supplied to one or both of an anode and a cathode, which face each other through a solid polymer electrolyte film, has been pressurized by using an oil free type compressor.
The solid polymer electrolyte film is generally composed of an ion-exchange film containing proton (hydrogen ion)-exchange groups, and acts as a proton conductive electrolyte in a water-containing state. So, by humidifying reaction gas to be supplied to the anode and the cathode, drying of the solid polymer electrolyte film has been prevented, whereby a high specific conductance of the solid polymer electrolyte film has been maintained, and the battery performance has been enhanced.
The well known lubrication methods for lubricating the sliding faces of the compressor (in particular, the displacement type compressor) include an oil free or solid lubrication method using a solid lubricant such as graphite or molybdenum disulfide, or a solid lubrication film (PTFE film), each having a low coefficient of friction, an oil lubrication method using oil or grease, and a water lubrication method using a water film.
In the above-described solid polymer electrolyte type fuel cell, due to the adhesion of an oil film to surfaces of the electrolyte, and to the anode and cathode thereof, the fuel cell reaction activity drops considerably. So, to pressurize reaction gas to be supplied to the cell, it has been necessary to use an oil free type compressor.
The oil free type compressor which lubricates the sliding faces of a cylinder bore or the like with solid lubricant or PTFE film, however, has the following problems. During operation, gas leakage may occur between the sliding faces, and the coefficient of friction thereof is great, so that it is difficult to increase the surface pressure (compression ratio) of the sliding faces. In addition, in order to restrain wear of the sliding members, the sliding speed, that is the number of revolutions, must be reduced. Consequently, to ensure a necessary supplying volume of reaction gas for the fuel cell, the size of the compressor must be made remarkably large, as compared to the normal oil lubricated type compressor, which results in a great increase in the power needed to drive the compressor, as compared to the normal oil lubricated type compressor.